This invention relates to a system for generating images magnetically. It relates more particularly to magnetic printing apparatus for making single and multiple copies of characters, graphics and the like.
In some proposed magnetic printing systems, a magnetic toner of ink is deposited on a suitably magnetized recording medium such as a tape or a drum to form a visible pattern. The magnetic material is then transferred by means of pressure and adhesion to paper stock. The ink or the paper stock may contain a wax or a thermoplastic binder which is liquified temporarily during or after the transfer and which thereafter provides a permanent bond between the ink and paper stock. Thus, using this technique, one can make reproductions of both text and pictorial subject matter.
Conventionally, the recording medium is selectively magnetized by a magnetic recording head. One proposed system of which we are aware employs a single pole recording head which scans across the recording drum line-by-line in the manner of a typewriter. During each scan line, the pole is energized in accordance with an input pattern to form a corresponding latent magnetic image on the drum. That system has the disadvantage of being quite slow. Other prior systems employ a recording head having a number of poles spaced along its length and covering the width of the magnetic drum. The head and drum are moved incrementally relative to one another and after each such movement, selected areas of the poles in the head are energized in turn to produce a linear pattern of magnetic dots on the drum. In other words, those systems scan each line electronically and advance from line to line mechanically.
Systems using multipole recording heads of the above type are potentially faster than those using single pole heads. However, they are not able to produce high quality reproductions. This is because the pole elements in the head are unavoidably large and, hence, the magnetized dot areas which they impress on the recording medium to form a pattern are spaced relatively far apart. Therefore, the reproductions of the pattern on the medium have relatively poor definition.
In addition, a practical system must be able to reproduce relatively wide patterns and long lines of text. This means that a very large number of independently switchable pole elements are required in the recording head in order to cover a complete line of text and these elements, including the required number of electronic switches, make the prior units quite complex and expensive to manufacture. Further, they still do not operate at a fast enough rate to meet many present-day requirements.
Accordingly, it is the object of the present invention to provide a system for generating magnetic images very quickly.
Another object of the invention is to provide a magnetic printing system whose reproductions are of a uniformly high quality.
A further object of the invention is to provide a magnetic printing system which operates at ultrahigh speeds
Yet another object of the invention is to provide a magnetographic printing system having a multipole printing head whose magnetically active centers are very closely spaced, on the order of 0.01 inch.
A further object of the invention is to provide a magnetographic printing system which is relatively easy and inexpensive to make.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope of the invention will be indicated in the claims.
Briefly, the present system impresses a latent image magnetically on a recording member such as a tape or drum using a special multipole recording head to be described presently. Then a magnetic ink or toner is applied to the drum. The toner adheres only to those portions corresponding to the dark parts of the latent image thereby reducing that image to a visible form. The magnetic toner is then transferred in the usual way by means or pressure and adhesion to paper brought into contact with the drum.
The printing head is composed of at least two layers of meandering electrical conductors, there being a number of separate conductors in each layer. These conductors are arranged so that selected segments of conductors in one layer are positioned above selected segments of conductors in the other layer at closely spaced points along the recording head. These points form the magnetically active centers of the head. In other words, each of these centers is defined by a selected pair of conductors, one from each layer.
At each of these centers, the corresponding segments of a conductor pair are arranged so that when electric currents are applied simultaneously to the conductor pair, two coinciding magnetic fields are generated which together are strong enough to change the magnetization of a corresponding point on the surface of the recording medium opposite the particular active center of the head. However, the recording medium has sufficiently high coercivity that its magnetization is not changed by only one field generated by the current flow in only one of the conductors of the pair. In other words, the magnetization of the recording medium is changed only at those centers of the head where there are coincident fields.
Using this coincident field addressing technique, selected pairs of conductors are energized in a timed manner so as to sweep out on the recording medium a latent magnetic image comprised of appropriately placed, closely spaced, magnetic dots. The medium is then dusted with a magnetic toner so that the latent image becomes visible. The toner may be transferred to a sheet of paper to make a hard copy of the image. Furthermore, since the recording medium retains the magnetic pattern impressed on it, after transfer of the magnetic toner, more toner can be applied repeatedly to the drum and transferred to successive sheets of paper to make multiple copies of the information on the recording medium.
The recording head in our system can have a single linear array of magnetically active centers extending across the recording member. In this event, the centers are activated electronically as the recording member advances so that the information is swept out line-by-line in the manner of a television raster without interlacing. Alternatively, the magnetically active centers may be arrayed in two dimensions in the head and be selectively energized in two dimensions, thus eliminating the need for any relative motion between the head and the recording member in order to record an image on the member.
The generation of coinciding magnetic fields to produce the magnetizing poles in the recording head, combined with matrix switching to activate the poles selectively, enables the present system to generate large, high-quality reproductions extremely rapidly. Yet the system is relatively inexpensive to make and easy to maintain.